US6885708B2 - Training prefix modulation method and receiver - Google Patents

Training prefix modulation method and receiver Download PDF

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US6885708B2
US6885708B2 US10/198,487 US19848702A US6885708B2 US 6885708 B2 US6885708 B2 US 6885708B2 US 19848702 A US19848702 A US 19848702A US 6885708 B2 US6885708 B2 US 6885708B2
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block
inter
interference
signal
data
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US20040013084A1 (en
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Timothy A. Thomas
Vijay Nangia
Kevin L. Baum
Frederick W. Vook
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Google Technology Holdings LLC
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Motorola Inc
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Priority to US10/198,487 priority Critical patent/US6885708B2/en
Priority to KR1020057000972A priority patent/KR100693778B1/ko
Priority to EP03765470A priority patent/EP1525698A4/de
Priority to PCT/US2003/020079 priority patent/WO2004010628A1/en
Priority to CNA038171163A priority patent/CN1669259A/zh
Priority to AU2003243786A priority patent/AU2003243786A1/en
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2602—Signal structure
    • H04L27/2605—Symbol extensions, e.g. Zero Tail, Unique Word [UW]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2602—Signal structure
    • H04L27/2605—Symbol extensions, e.g. Zero Tail, Unique Word [UW]
    • H04L27/2607—Cyclic extensions
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
    • H04L2025/0335—Arrangements for removing intersymbol interference characterised by the type of transmission
    • H04L2025/03375—Passband transmission
    • H04L2025/03414—Multicarrier
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
    • H04L2025/03433—Arrangements for removing intersymbol interference characterised by equaliser structure
    • H04L2025/03439—Fixed structures
    • H04L2025/03522—Frequency domain
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0224—Channel estimation using sounding signals
    • H04L25/0226—Channel estimation using sounding signals sounding signals per se

Definitions

  • the present invention generally relates to the field of communication systems. More specifically, the invention relates to communication systems implementing frequency-domain-oriented modulation methods (“FDMM”) (e.g., orthogonal frequency division multiplexing (“OFDM”), spread OFDM (“SOFDM”) or multi-carrier code division multiple access (“MC-CDMA”), single carrier with cyclic prefix (“CP-SC”), cyclic prefix code division multiple access (“CP-CDMA”), and interleaved frequency division multiple access (“IFDMA”)).
  • FDMM frequency-domain-oriented modulation methods
  • OFDM orthogonal frequency division multiplexing
  • SOFDM spread OFDM
  • MC-CDMA multi-carrier code division multiple access
  • CP-SC single carrier with cyclic prefix
  • CP-CDMA cyclic prefix code division multiple access
  • IFDMA interleaved frequency division multiple access
  • Single carrier with cyclic prefix (“CP-SC”) insertion is a signal format known in the art for facilitating frequency-domain equalization. This is due to the cyclic prefix insertion causing the convolution of the CP-SC signal with a multipath channel to appear circular at the receiver (this can also be said to restore orthogonality between the frequency domain bins or subcarriers of a frequency domain representation of the signal). This circular appearance of the channel (also known as a circular channel) enables the use of low complexity frequency-domain equalization of the single carrier signal.
  • a disadvantage of conventional CP-SC is that the receiver discards the received cyclic prefix prior to detection, resulting in a waste of the energy relating to the cyclic prefixes.
  • Training prefix single carrier is a means to recover the lost energy relating to the cyclic prefixes.
  • Training prefix single carrier replaces the traditional cyclic prefixes with a block of known symbols known as the training prefix (i.e., each block of data symbols has a training prefix sent before and after it, where the one after it is actually a prefix for a following data block).
  • the training prefix is the same for each block of data symbols. These training symbols may be used to estimate the channel or improve the tracking in time of the channel.
  • prior art methods for recovering the data symbols may be inefficient due to the need of taking a larger fast fourier transform (“FFT”) that encompasses the training prefixes.
  • FFT fast fourier transform
  • One form of the invention is a method for reconstructing a signal including a data block having a first inter-block-interference and a training block having a second inter-block-interference.
  • the data block is reconstructed to exclude the first inter-block-interference and to include the second inter-block-interference.
  • a second form of the invention is another method for reconstructing a signal including a data block having a first inter-block-interference and a training block having a second inter-block-interference.
  • the training block is replaced with a null block, and the null block is constructed to include the second inter-block-interference.
  • the data block can be reconstructed to exclude the first inter-block interference.
  • a third form of the invention is a method for processing a signal propagating through a channel.
  • the signal includes a data block and a training block with the data block including information and a first inter-block-interference, and the training block including a second inter-block-interference.
  • one or more reconstructions of the data block to exclude the first inter-block-interference and to include the second inter-block-interference are selectively executed.
  • the reconstructed data block can then be processed further to recover information in the data block.
  • a fourth form of the invention is a method for creating a multicarrier signal block with a training extension, which can be transmitted over a channel and used by a receiver in accordance with one of the other forms of the invention.
  • FIG. 1 illustrates a timing diagram of a single-carrier transmitted signal having cyclic prefixes as known in the art
  • FIG. 2 illustrates a timing diagram of a transmission and a reception of a FDMM signal having training blocks in accordance with the present invention
  • FIG. 3 illustrates a timing diagram of a first embodiment of a reconstruction of the received signal of FIG. 2 in accordance with the present invention
  • FIG. 4 illustrates a timing diagram of a second embodiment of a reconstruction of the received signal of FIG. 2 in accordance with the present invention
  • FIG. 5 illustrates a block diagram of one embodiment of a receiver in accordance with the present invention
  • FIG. 6 illustrates a flowchart representative of one embodiment of a signal detection and decoding method in accordance with the present invention
  • FIG. 7 illustrates a flowchart representative of a first embodiment of a signal detection method in accordance with the present invention
  • FIG. 8 illustrates a flowchart representative of one embodiment of a signal reconstruction method in accordance with the present invention
  • FIG. 9 illustrates a flowchart representative of a second embodiment of a signal detection method in accordance with the present invention.
  • FIG. 10 illustrates a flowchart representative of one embodiment of a signal remodulation method in accordance with the present invention.
  • the invention relates to communication systems implementing frequency-domain-oriented modulation methods (“FDMM”) (e.g., orthogonal frequency division multiplexing (“OFDM”), spread OFDM (“SOFDM”) or multi-carrier code division multiple access (“MC-CDMA”) or code division multiplexed OFDM (CDOFDM), single carrier with cyclic prefix (“CP-SC”), cyclic prefix code division multiple access (“CP-CDMA”), and interleaved frequency division multiple access (“IFDMA”)).
  • FDMM frequency-domain-oriented modulation methods
  • OFDM orthogonal frequency division multiplexing
  • SOFDM spread OFDM
  • MC-CDMA multi-carrier code division multiple access
  • CDMA code division multiplexed OFDM
  • CP-SC single carrier with cyclic prefix
  • CP-CDMA cyclic prefix code division multiple access
  • IFDMA interleaved frequency division multiple access
  • FIG. 1 illustrates a cyclic prefix single-carrier transmitted signal 10 as known in the art.
  • the signal 10 includes a baud 11 a consisting of a cyclic prefix 12 a and a data block 13 a where cyclic prefix 12 a is a repetition of the last v samples (cyclic prefix of length v) of the data block 13 a .
  • the cyclic prefix may also be referred to as a cyclic extension, and the samples between data blocks 13 a and 13 b can also be referred to as a guard period.
  • the baud 11 a is followed by a baud 11 b consisting of a cyclic prefix 12 b and a data block 13 b .
  • the baud 11 b is followed by additional bauds (not shown) also consisting of cyclic prefixes and data blocks.
  • the cyclic prefix 12 a and the cyclic prefix 12 b , as well as the other cyclic prefixes of the signal 10 have a length of v samples.
  • the data block 13 a and the data block 13 b , as well as the other data blocks of signal 10 include N number of data samples.
  • a receiver of the signal 10 usually ignores the channel outputs corresponding to the cyclic prefix 12 a , the cyclic prefix 12 b and the other cyclic prefixes of the signal 10 . This results in a waste of energy relating to cyclic prefix 12 a , the cyclic prefix 12 b and the other cyclic prefixes of the signal 10 .
  • a single-carrier TDM/TDMA transmission format has replaced the cyclic prefix 12 a and the cyclic prefix 12 b with a known sequence. If a receiver for this format uses a discrete Fourier transform of size N+v, including for example the data block 13 a and the subsequent prefix 12 b , then the entire block of N+v samples appears to have a conventional cyclic prefix 12 a , provided the sequence used in the cyclic prefix 12 a is the same as the sequence used in the cyclic prefix 12 b (and likewise for all subsequent baud intervals).
  • the present invention enables different known sequences (training blocks) to be used for different data blocks, it enables the discrete Fourier transform size to remain at N in some embodiments (rather than N+v), and it provides methods that can be used with multicarrier signals (such as OFDM) as well as other FDMMs.
  • FIG. 2 illustrates a FDMM with training blocks signal 20 a .
  • the signal 20 a includes a baud 21 a consisting of a training block in the form of a training prefix 22 a , and a data block 23 a where the training prefix 22 a is any known signal pattern of length v samples.
  • the baud 21 a is followed by a baud 21 b consisting of a training block in the form of a training prefix 22 b , and a data block 23 b .
  • the baud 21 b is followed by a baud 21 c consisting of a training block in the form of a training prefix 22 c , and a data block 23 c .
  • the baud 21 c can be followed by additional bauds (not shown).
  • the training prefixes 22 a , 22 b , and 22 c can be different from each other, and training prefixes for additional forms of modulation (e.g., OFDM) are enabled.
  • the training prefix 22 a , the training prefix 22 b and the training prefix 22 c , as well as the other training prefixes of the signal 20 a preferably all have the same length of v samples, but are not required to have the same length.
  • the data block 23 a , the data block 23 b , and the data block 23 c , as well as the other data blocks of signal 20 a preferably all have the same length of N samples, but are not required to have the same length.
  • a multicarrier signal is generated and formatted in accordance with the baud format of FIG. 2 .
  • This embodiment creates a multicarrier signal block with a training extension, which can be transmitted over a channel and used by a receiver in accordance with one of the other receiver-related or reconstruction-related embodiments of the present invention as illustrated in FIGS. 5-10 .
  • a multicarrier signal block with a training extension is generated by extending a multicarrier signal block with a known training block, where the position of the extension is: A) a prefix, B) a postfix, C) a combination of a prefix and a postfix.
  • a multicarrier signal block can be represented by a data block in FIG. 2 .
  • a data block of FIG. 2 is preferably a time domain signal which represents a block of frequency domain symbols.
  • a time domain signal which represents a block of frequency domain symbols is typically generated by taking an inverse discrete or fast fourier transform of the block of frequency domain symbols, as is known in the art for OFDM.
  • a signal 20 b is a version of the signal 20 a at the output of a multi-path channel in communication with a receiver with interference contributions due to inter-block-interference (IBI) such as training IBI 24 a , a data IBI 25 a , a training IBI 24 b , a data IBI 25 b and a training IBI 24 c .
  • IBI inter-block-interference
  • the received data block 23 a ′ is the result of the channel filtering both the transmitted training prefix 22 a and the transmitted data block 23 a .
  • the received training prefix block 22 b ′ is the result of the channel filtering both the transmitted data block 23 a and the training prefix 22 b .
  • the channel filters the data block 23 a a portion of it is received during training prefix block 22 b ′, and this portion is called the data IBI 25 a .
  • the received data block 23 b ′ is the result of the channel filtering both the transmitted training prefix 22 b and the transmitted data block 23 b .
  • the received training prefix block 22 c ′ is the result of the channel filtering both the transmitted data block 23 b and the training prefix 22 c .
  • the channel filters the data block 23 b a portion of it is received during training prefix block 22 c ′, and this portion is called the data IBI 25 b .
  • the received data block 23 c ′ is the result of the channel filtering both the transmitted training prefix 22 c and the transmitted data block 23 c .
  • the channel filters the training prefix 22 c a portion of it is received during data block 23 c ′, and this portion is called the training IBI 24 c .
  • the loss of the circular appearance of the channel within the data block results in a loss of subcarrier orthogonality and a corresponding degradation in the performance of the receiver.
  • a data block is not intended to imply a limitation on the contents of a data block (such as 23 a in FIG. 2 ) to a particular type of information.
  • a data block may include one or more types of information such as user data, pilot symbols, control information, signaling, link maintenance information, broadcast information, and so forth, and such information may be coded or uncoded.
  • FIG. 3 illustrates a first embodiment in accordance with the present invention of a reconstruction of the signal 20 b ( FIG. 2 ) to a signal 20 d.
  • the signal 20 b is reconstructed to a signal 20 c that excludes the training IBI 24 a from data block 23 a ′, the training IBI 24 b from data block 23 b ′, and the training IBI 24 c from data block 23 c ′.
  • the signal 20 c is reconstructed to signal 20 d that includes the data IBI 25 a within a data block 23 a ′′′, the data IBI 25 b within a data block 23 b ′′′, and to include the data IBI 25 c within a data block 23 c ′′′.
  • each of the reconstructed data blocks 23 a ′′′, 23 b ′′′, and 23 c ′′′ now appear to have been propagated over a circular channel.
  • the described steps are given in the preferred order, but the principles of linearity and superposition may allow the order of the steps to be changed from the described order in the present embodiment or other embodiments.
  • the data IBI can be reconstructed as the first step and the training IBI can be removed as the second step.
  • the reconstruction as illustrated in FIG. 3 can be iterated to further refine the circular appearance of the channel over one or more of the data blocks 23 a ′′′- 23 c ′′′ of the signal 20 d , as will be described later.
  • the depicted embodiment includes three sequential data blocks, each with a training prefix, and the signal reconstruction is described for all three data blocks.
  • the invention is not limited to reconstructing the complete group of data blocks as has been described.
  • a sequential implementation of the reconstruction can operate independently on each data block.
  • different data blocks may be addressed to different users, and in such a case it may not be necessary to reconstruct data blocks that are addressed to a different user.
  • FIG. 4 illustrates a second embodiment in accordance with the present invention of a reconstruction of the signal 20 b ( FIG. 2 ) to a signal 20 f .
  • the signal 20 b is reconstructed to a signal 20 e having training prefix 22 a , training prefix 22 b , and training prefix 22 c replaced by a null prefix 26 a , a null prefix 26 b , and a null prefix 26 c , respectively
  • the null prefix also referred to as a null block, is a block of v zeros.
  • the training IBI 24 a is excluded from data block 23 a ′
  • the training IBI 24 b is excluded from data block 23 b ′
  • the training IBI 24 c is excluded from data block 23 c ′.
  • the signal 20 e is reconstructed to signal 20 f that includes the data IBI 25 a within the null prefix 26 b ′, the data IBI 25 b within the null prefix 26 c ′.
  • each of the combined blocks 23 a ′′′ and 26 b ′, and 23 b ′′′ and 26 c ′ now appear to have been propagated over a circular channel.
  • the depicted embodiment includes three sequential data blocks, each with a training prefix, and the signal reconstruction is described for all three data blocks.
  • the invention is not limited to reconstructing the complete group of data blocks as has been described.
  • a sequential implementation of the reconstruction can operate independently on each data block.
  • different data blocks may be addressed to different users, and in such a case it may not be necessary to reconstruct data blocks that are addressed to a different user.
  • FIG. 5 illustrates one embodiment of a receiver 30 in the accordance with the present invention.
  • the receiver 30 includes an antenna 31 , a signal buffer 32 , a signal demodulation and detection (“SDD”) module 33 , a channel decoder 34 , a switch 35 a , a signal remodulator 36 , a channel estimator 37 , a signal resynthesizer 38 , and a switch 35 b .
  • SDD signal demodulation and detection
  • receiver 30 From the operational description of the receiver 30 , those having ordinary skill in the art will appreciate a processing by the receiver 30 in accordance with the present invention of a signal having training blocks in the form of either a training prefix or a training postfix or a combination of a training prefix and a training postfix.
  • the signal buffer 32 is any type of memory for receiving and storing the signal 20 b ( FIG. 1 ) or a portion thereof upon receipt thereof by the antenna 31 .
  • the received signal 20 b may be processed by a RF front-end and downconverted from RF to baseband and/or sampled prior to the signal buffer 32 .
  • the receiver 30 executes a signal decoding method in accordance with the present invention.
  • FIG. 6 illustrates a flowchart 40 as a representation of the signal decoding method.
  • the receiver 30 may process the received data according to flowchart 40 on a per data block basis or on multiple data blocks or a combination thereof. Flowchart 40 can be repeated for subsequent data blocks.
  • the description below exemplifies the detection and decoding process for a data block such as 23 a (FIG. 2 ).
  • FIG. 6 illustrates the flowchart 40 .
  • the channel estimator module 37 either computes or retrieves a previously determined estimate of a channel pulse response (“CPR”) p l through which the data block 23 a of signal 20 a ( FIG. 2 ) propagates resulting in the received data block 23 a ′ of signal 20 b (FIG. 2 ).
  • CPR channel pulse response
  • the (CPR) p l is a combined response of transmit filters, the channel and receiver filters and is assumed to be of length M+1, where the training prefix length v is preferably chosen such that M ⁇ v.
  • the SDD module 33 ascertains whether to execute a signal reconstruction of the data block 23 a ′ based on the characteristics of the transmitted signal and the available receiver processing power. If the SDD module 33 determines that an execution of a signal reconstruction of the data block 23 a ′ is not warranted, the SDD module 33 proceeds to a stage S 46 of the flowchart 40 to implement a flowchart 70 representative of a first embodiment of an information detection method of the present invention.
  • the SDD module 33 determines that an execution of a signal reconstruction of the data block 23 a ′ is warranted, the SDD module 33 proceeds to a stage S 48 of the flowchart 40 to implement a flowchart 90 representative of one embodiment of a signal reconstruction method of the present invention.
  • the operational thresholds for the characteristics of the transmitted signal and the available receiver processing power that warrant a signal reconstruction of the signal 20 b are dependent upon operational specifications of receiver 30 and are therefore not specified with this description of the flowchart 40 .
  • those having ordinary skill in the art will appreciate a proper association of such operational thresholds to a receiver fabricated in accordance with the present invention.
  • the decision of whether to perform signal reconstruction can be made at the time the receiver is being designed, taking into account various factors such as the available processing power and the performance improvement that would be provided by reconstruction, which can be estimated using computer simulations of the receiver performance.
  • FIG. 7 illustrates a flowchart 70 for detecting channel symbols (e.g., hard symbols, hard bits, soft symbols and/or soft bits) within data block 23 a ′.
  • FFT fast Fourier transform
  • the SDD module 33 conventionally equalizes the signal within the frequency domain.
  • Stages S 72 -S 76 represent a linear frequency domain equalization of the signal.
  • stages S 72 -S 76 can be replaced by stages representative of a linear transversal time-domain equalization, or another appropriate form of equalization.
  • the training prefix i.e., a guard period
  • the SDD module 33 conventionally detects the channel symbols (e.g., by outputting one or more of: soft or un-sliced symbols, hard or sliced symbols, soft bits, hard bits).
  • the flowchart 70 is terminated upon a completion of stage S 82 with the result being a detection of the channel symbols within data block 23 a ′.
  • the receiver 30 proceeds to stage S 54 of the flowchart 40 to ascertain whether to improve upon the performance of the receiver 30 by using iteration.
  • FIG. 8 illustrates the flowchart 90 .
  • the SDD module 33 generates or receives an estimate of the training IBI 24 a .
  • the SDD module 33 Upon completion of the stage S 94 , the SDD module 33 proceeds to a stage S 96 of the flowchart 90 to generate an estimate of the data IBI 25 a .
  • the remodulated signal ⁇ circumflex over (x) ⁇ l (as elaborated later) is an estimate of the data transmitted within data block 23 a .
  • the estimates of the CPR, ⁇ circumflex over (p) ⁇ l a , ⁇ circumflex over (p) ⁇ l b , ⁇ circumflex over (p) ⁇ l c can be the current iteration CPR estimate, or any one of the previous iteration CPR estimates.
  • the feedback gain ⁇ is set to 0 on the first iteration.
  • the total noise power is increased.
  • an iterative, decision aided IBI estimation method may be used.
  • small values of alpha can be used thereby introducing less error due to incorrect symbol/bit decisions, while improving the receiver performance as the estimator noise is reduced.
  • the value of alpha can be increased (preferred) making it closer to one, further reducing the estimator noise and improving receiver performance.
  • an initial signal detection based on conventional methods can be performed to estimate the remodulated signal ⁇ circumflex over (x) ⁇ l prior to the first iteration, thus enabling the option of setting ⁇ >0 for the first iteration.
  • This alternate embodiment is anticipated to be useful when the channel pulse response is much smaller than the cyclic prefix length.
  • the SDD module 33 Upon completion of the stage S 96 , the SDD module 33 proceeds to a stage S 98 of the flowchart 90 ascertain whether to implement a null prefix reconstruction. When the SDD module 33 determines a null prefix reconstruction is not warranted, the SDD module 33 proceeds to a stage S 100 of the flowchart 90 to add the estimate of the data IBI 25 a to the data block 23 a ′′ to thereby yield data block 23 a ′′′ of the signal 20 d (FIG.
  • the SDD module 33 proceeds to a stage S 104 of the flowchart 90 to add the estimate of the data IBI 25 a to the null prefix 26 b , to thereby yield a corresponding portion of the signal 20 f (FIG. 4 ).
  • the null prefix 26 b ′ with the data IBI 25 a is obtained by subtracting out an estimate of the training prefix block 22 b′.
  • stage S 50 the receiver 30 proceeds to a stage S 50 to ascertain whether a null prefix reconstruction was implemented during stage S 48 .
  • the receiver 30 proceeds to stage S 46 to detect information within data block 23 a ′′′ of signal 20 f ( FIG. 4 ) in a manner analogous to the detection of information within data block 23 a ′ of signal 20 b as described in connection with FIG. 7 .
  • the receiver 30 proceeds to stage S 54 to ascertain whether to improve upon the performance of the receiver 30 by using iteration.
  • FIG. 9 illustrates the flowchart 110 for detecting channel symbols (e.g., hard symbols, hard bits, soft symbols and/or soft bits) within data block 23 a ′′′ of signal 20 d .
  • the SDD module 33 removes training prefix 22 a (i.e., guard period) of the signal 20 e .
  • the SDD module 33 conventionally equalizes the signal within the frequency domain.
  • the equalization can be a conventional complex channel gain compensation on each subcarrier.
  • stage S 120 of the flowchart 110 the SDD module 33 conventionally detects the channel symbols.
  • the flowchart 110 is terminated upon a completion of stage S 120 with the result being a detection of the channel symbols within data block 23 a ′′′ of signal 20 d .
  • Stages S 114 -S 118 represent a linear frequency domain equalization of the signal. If the transmitted signal is a single carrier signal, in an alternative embodiment, stages S 114 -S 118 can be replaced by stages representative of a linear transversal time-domain equalization, a decision feedback equalization, a maximum likelihood sequence estimator, or another known form of equalization.
  • stage S 52 the receiver 30 proceeds to stage S 54 to ascertain whether to improve upon the performance of the receiver 30 by using iteration.
  • the receiver 30 proceeds to a stage S 56 of the flowchart 40 when iteration is not selected.
  • the channel decoder 34 decodes the detected channel symbols.
  • the channel decoder 34 may include additional conventional aspects such as de-interleaving and buffering of information that is part of a codeword, and that a codeword may span more than one data block.
  • the receiver 30 then proceeds to terminate flowchart 40 .
  • the receiver 30 proceeds to a stage S 58 of the flowchart 40 when iteration is selected to ascertain whether decoded channel symbols are used in the iteration. For the case when the decoded channel symbols are used, the receiver 30 proceeds to a stage S 60 of the flowchart 40 to decode the detected channel symbols. Additionally, the switch 35 a is set in a position to establish communication between the channel decoder 34 and the signal remodulator 36 . Note that the channel decoder 34 may include additional conventional aspects such as de-interleaving and buffering of information that is part of a codeword, and that a codeword may span more than one data block. Additionally, the switch 35 b is set in a position to establish communication between the signal resynthesiser 38 and the SDD module 33 . The receiver 30 can therefore proceed to a stage S 62 of the flowchart 40 to implement a flowchart 130 representative on one embodiment of a signal remodulation method in accordance with present invention.
  • the switch 35 a when selected to not use the decoded channel symbols, the switch 35 a is set in a position to establish communication between the SDD module and the signal remodulator 36 . Additionally, the switch 35 b is set in a position to establish communication between the signal resynthesiser 38 and the SDD module 33 .
  • the receiver 30 can therefore proceed to a stage S 62 of the flowchart 40 to implement a flowchart 130 representative on one embodiment of a signal remodulation method in accordance with present invention.
  • FIG. 10 illustrates the flowchart 130 .
  • the signal remodulator 36 remodulates the detected/decoded channel symbols (hard symbols, hard bits, soft symbols and/or soft bits or a combination thereof). This remodulation involves an initial re-encoding of the information if the signal remodulator 36 is receiving information from the channel decoder 34 .
  • the samples at the output of signal remodulator 36 are estimates of the transmitted data block 23 a .
  • the preferred embodiment uses null prefixes instead of training prefixes in the remodulation stage 36 (note that null prefixes can be used in the remodulation stage 36 even though the transmitted signal may contain a training prefix) as it results in lower computational complexity for equivalent performance.
  • the signal remodulator may only re-modulate the portion of the signal needed for subsequent processing.
  • stage S 132 the receiver 30 proceeds to a stage S 134 of the flowchart 130 to ascertain whether channel estimator 37 will need to update the channel estimate during a stage S 136 of the flowchart 130 , or use the previous iteration channel estimate. If the previous iteration channel estimate is to be used, then flow proceeds to stage S 138 . If the channel estimate is to be updated, then flow proceeds to stage S 136 , where the channel estimate is updated. Then in stage S 138 , both the data inter-block interference and the training inter-block interference are estimated according to equation 5 and 3 respectively.
  • stage S 138 The flowchart 130 is terminated upon completion of stage S 138 .
  • the choice of waveforms for the training prefix can be any signal such as a reduced symbol duration OFDM training symbol (short OFDM symbol) or a single carrier training sequence.
  • a signal with a close to flat amplitude spectrum and low peak-to-average power ratio is desirable as it enables the channel estimate errors to be frequency independent and may allow the training prefix to be transmitted at a higher power level than the data block while maintaining the same power amplifier backoff requirement.
  • the present invention also enables the training prefix waveform to be different for different data blocks, except for the case of OFDM-type signals where signal reconstruction is not used (i.e., “no” is selected in S 44 of FIG. 6 ).
  • the training prefixes be identical for adjacent data blocks, so that the equalizer performance will be improved. Since the present invention can enable the use of different training prefixes for different data blocks, it can be applied to CDMA systems where the training prefix is a pilot block multiplied by a long code or scrambling code or PN sequence. In this case, the long code/scrambling code/PN sequence causes the transmitted training prefixes to be different even if they were the same prior to applying the long code/scrambling code/PN sequence.
  • the proposed methods can also be used when a data slot is preceded and/or followed by an idle slot. In this case, the idle slot is treated as a training prefix/postfix containing zeros (null prefix or postfix), as appropriate.
  • the signal reconstruction can also be done in the frequency domain because the FFT operation (or equivalent frequency-domain transform) is a linear transform.
  • the data block 23 a ′ FIG. 2
  • the frequency-domain equivalent of the training IBI 24 a can be subtracted from the frequency domain representation of data block 23 a ′ and finally the frequency-domain equivalent of the data IBI 25 a can be added to the result.
  • Each component of the receiver 30 may be implemented in hardware (analog or digital), software, or any combination of hardware and software.
  • Those having ordinary skill in the art will appreciate a sequential operation of the components of the receiver 30 (e.g., in a software implementation) and a concurrent operation of each component of the receiver 30 (e.g., in a hardware implementation).
  • the receiver 30 was described herein in the context of a complete implementation of the flowchart 40 to facilitate a comprehensive understanding of the present invention, in practice, a significant number of receivers will be designed in accordance with the present invention to take a particular path through the flow chart 40 .
  • the yes/no decisions of the stages S 44 , S 50 , S 54 , and/or S 58 can be predetermined during a design phase of such receivers in view of various factors, including, but not limited to, processing power, battery drain, expected channel conditions, and the characteristics of the transmitted signal (e.g., OFDM, single carrier).
  • the yes/no decisions of the stages S 98 and/or S 134 can be predetermined during a design phase of such receivers.
  • a predetermined path through the various stages of the flow chart 40 can follow the illustrated stage sequence as described herein or an alternative stage sequence that may include concurrent execution of some of the stages. The same holds true for the various stages of the flow chart 98 and the various stages of the flow chart 134 .
  • the scope of the claims are therefore intended to encompass a practical implementation of the present invention as explained in the preceding sentences.

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EP03765470A EP1525698A4 (de) 2002-07-18 2003-06-26 Verfahren und empfänger zur modulation eines trainingspräfixes
PCT/US2003/020079 WO2004010628A1 (en) 2002-07-18 2003-06-26 Training prefix modulation method and receiver
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KR100693778B1 (ko) 2007-03-12
US20040013084A1 (en) 2004-01-22
KR20050026490A (ko) 2005-03-15
CN1669259A (zh) 2005-09-14
EP1525698A1 (de) 2005-04-27
AU2003243786A1 (en) 2004-02-09
WO2004010628A1 (en) 2004-01-29

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